Exhaust turbine power generating system

ABSTRACT

An exhaust turbine power generating system includes an internal combustion engine including a first exhaust opening portion and a second exhaust opening portion for each of cylinders, an exhaust turbine power generator configured to generate electric power by rotating a turbine by using exhaust gas from the internal combustion engine, a first exhaust pipe configured to connect the first exhaust opening portion and an inlet portion of the turbine, and a second exhaust pipe configured to connect the second exhaust opening portion and a turbine downstream side exhaust pipe downstream of the turbine, not via the turbine. The volume of the first exhaust pipe is smaller than the volume of the second exhaust pipe.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2017-035129 filed on Feb. 27, 2017 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an exhaust turbine power generating system that generates electric power by using exhaust gas from an internal combustion engine.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2015-21448 (JP 2015-21448 A) discloses an exhaust turbine power generating system that generates electric power by using exhaust energy of an internal combustion engine. An exhaust gas flow path in the exhaust turbine power generating system is divided into two systems. Exhaust gas in a blowdown stream is supplied to a turbine unit in an exhaust turbine power generator through a first exhaust gas flow path. The first exhaust gas flow path upstream of the turbine unit is provided with an exhaust receiver that stores exhaust energy. Exhaust gas in a scavenging stream flows through a second exhaust gas flow path while bypassing the exhaust receiver and the turbine unit.

Japanese Unexamined Patent Application Publication No. 2010-24972 (JP 2010-24972 A) discloses an internal combustion engine with a turbocharger. The internal combustion engine is provided with a first exhaust path that leads to a turbine of the turbocharger, a second exhaust path that does not pass through the turbine, and EGR paths that extend from the exhaust paths toward intake paths. The EGR paths include a first EGR path that is connected to the first exhaust path upstream of the turbine and a second EGR path that is connected to the second exhaust path.

SUMMARY

In order to further increase the turbine work in an exhaust turbine power generating system, it is needed to further increase the expansion ratio of a turbine. In order to further increase the expansion ratio of the turbine, it is needed to further increase the pressure of gas at a turbine inlet. However, in the exhaust turbine power generating system disclosed in JP 2015-21448 A, the first exhaust gas flow path upstream of the turbine unit is provided with the exhaust receiver having a predetermined volume. In a case where such an exhaust receiver is present, the pressure of exhaust gas in a blowdown stream is unlikely to increase, that is, the pressure of gas at the turbine inlet is unlikely to increase. As a result, there is a decrease in turbine work.

The present disclosure provides a technique with which it is possible to improve the turbine work in an exhaust turbine power generating system including a two-system exhaust path.

An aspect of the present disclosure relates to an exhaust turbine power generating system that includes an internal combustion engine, an exhaust turbine power generator, a first exhaust pipe, and a second exhaust pipe. The internal combustion engine includes a first exhaust opening portion and a second exhaust opening portion for each of cylinders. The exhaust turbine power generator is configured to generate electric power by rotating a turbine by using exhaust gas from the internal combustion engine. The first exhaust pipe is configured to connect the first exhaust opening portion and an inlet portion of the turbine. The second exhaust pipe is configured to connect the second exhaust opening portion and a turbine downstream side exhaust pipe downstream of the turbine, not via the turbine. The volume of the first exhaust pipe is smaller than the volume of the second exhaust pipe.

In the exhaust turbine power generating system according to the aspect of the present disclosure, in the case of the first exhaust pipe and the second exhaust pipe connected to the same cylinder, the length of the first exhaust pipe may be smaller than the length of the second exhaust pipe.

In the exhaust turbine power generating system according to the aspect of the present disclosure, for each of the cylinders, the first exhaust opening portion may be disposed closer to the inlet portion of the turbine than the second exhaust opening portion.

In the exhaust turbine power generating system according to the aspect of the present disclosure, in a case where a direction from the internal combustion engine to the turbine is a first direction and a direction intersecting the first direction is a second direction, the second exhaust pipe may be disposed to be offset from the first exhaust pipe while being closer to the second direction side than the first exhaust pipe.

In the exhaust turbine power generating system according to the aspect of the present disclosure, the diameter of the first exhaust pipe may be smaller than the diameter of the second exhaust pipe.

In the exhaust turbine power generating system according to the aspect of the present disclosure, the area of the first exhaust opening portion may be larger than the area of the second exhaust opening portion.

According to the aspect of the present disclosure, an exhaust path is divided into two systems. The first exhaust pipe is used to guide exhaust gas to the turbine of the exhaust turbine power generator. Meanwhile, the second exhaust pipe is used to discharge exhaust gas in such a manner that the exhaust gas is discharged without passing through the turbine. In addition, the volume of the first exhaust pipe is smaller than the volume of the second exhaust pipe. Since the volume of the first exhaust pipe for guiding exhaust gas to the turbine is relatively small, the pressure of gas at a turbine inlet likely to increase and an increase in pressure of gas becomes large. That is, it is possible to effectively guide energy of exhaust gas to the turbine and to further increase the turbine input work. As a result, the expansion ratio of the turbine increases and the turbine work in the exhaust turbine power generating system is improved.

According to the aspect of the present disclosure, the length of the first exhaust pipe is smaller than the length of the second exhaust pipe. Therefore, it is easy to set the volume of the first exhaust pipe to be smaller than the volume of the second exhaust pipe.

According to the aspect of the present disclosure, for each of the cylinders, the first exhaust opening portion is disposed closer to the inlet portion of the turbine than the second exhaust opening portion. When the exhaust opening portions are arranged as described above, it is easy to set the length of the first exhaust pipe to be smaller than the length of the second exhaust pipe. That is, it is easy to set the volume of the first exhaust pipe to be smaller than the volume of the second exhaust pipe.

According to the aspect of the present disclosure, the second exhaust pipe is disposed to be offset from the first exhaust pipe while being closer to the second direction side than the first exhaust pipe, the second direction intersecting the first direction which is a direction toward the turbine. That is, the second exhaust pipe bypasses the shortest route to the turbine. Therefore, it is possible to dispose the first exhaust pipe in a space for the shortest route to the turbine, and thus it is possible to set the length of the first exhaust pipe to be smaller than the length of the second exhaust pipe. That is, it is easy to set the volume of the first exhaust pipe to be smaller than the volume of the second exhaust pipe.

According to the aspect of the present disclosure, the diameter of the first exhaust pipe is smaller than the diameter of the second exhaust pipe. Therefore, it is easy to set the volume of the first exhaust pipe to be smaller than the volume of the second exhaust pipe.

According to the aspect of the present disclosure, the area of the first exhaust opening portion is larger than the area of the second exhaust opening portion. Since the area of the first exhaust opening portion is increased, the area of a curtain area immediately after an exhaust valve is lifted is increased. Accordingly, the amount of exhaust gas that flows into the first exhaust pipe at an initial stage of an exhaust stroke is further increased and the pressure of gas in the first exhaust pipe is further increased. As a result, the turbine work is further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic diagram illustrating an example of the configuration of an exhaust turbine power generating system according to a first embodiment of the present disclosure;

FIG. 2 is a graph illustrating valve control in the exhaust turbine power generating system according to the first embodiment of the present disclosure;

FIG. 3 is a graph for describing a general change in exhaust pressure;

FIG. 4 is a graph illustrating the dependency of turbine input work on the exhaust volume;

FIG. 5 is a schematic diagram illustrating the characteristics of the exhaust turbine power generating system according to the first embodiment of the present disclosure;

FIG. 6 is a schematic diagram illustrating an example of the configuration of an exhaust turbine power generating system according to a second embodiment of the present disclosure;

FIG. 7 is a schematic diagram illustrating another example of the configuration of the exhaust turbine power generating system according to the second embodiment of the present disclosure;

FIG. 8 is a sectional view for describing the characteristics of an exhaust turbine power generating system according to a third embodiment of the present disclosure;

FIG. 9 is a side view for describing the characteristics of the exhaust turbine power generating system according to the third embodiment of the present disclosure; and

FIG. 10 is a schematic diagram for describing the characteristics of an exhaust turbine power generating system according to a fourth embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described with reference to attached drawings.

1. First Embodiment 1-1. Basic Configuration

FIG. 1 is a schematic diagram illustrating an example of the configuration of an exhaust turbine power generating system 1 according to a first embodiment of the present disclosure. The exhaust turbine power generating system 1 includes an internal combustion engine 10 (engine), an exhaust turbine power generator 50, an electric device 70, and a control device 100 as main components.

The internal combustion engine 10 includes a cylinder 11 (combustion chamber) in which combustion is performed. Although one cylinder 11 is illustrated in FIG. 1 as a representative, the number of cylinders 11 is optional. In the cylinder 11, a piston (not shown) is provided such that the piston can reciprocate vertically. The vertical reciprocating motion of the piston results in intake and exhaust.

An intake pipe 20 (intake port) is provided to supply intake gas to the cylinder 11. Opening portions of the intake pipe 20 with respect to the cylinder 11 are intake opening portions 21. That is, the intake pipe 20 is connected to the cylinder 11 via the intake opening portions 21. The intake opening portions 21 are provided with an intake valve (not shown) such that the intake valve can be opened and closed. Supply of intake gas to the cylinder 11 is controlled by controlling opening and closing of the intake valve. In the middle of the intake pipe 20, a throttle valve 25 for adjusting the amount of intake gas is disposed.

An exhaust pipe 30 (exhaust port) is provided to discharge exhaust gas from the cylinder 11. Opening portions of the exhaust pipe 30 with respect to the cylinder 11 are exhaust opening portions 31. That is, the exhaust pipe 30 is connected to the cylinder 11 via the exhaust opening portions 31. The exhaust opening portions 31 are provided with an exhaust valve (not shown) such that the exhaust valve can be opened and closed. Discharge of exhaust gas from the cylinder 11 is controlled by controlling the opening and closing of the exhaust valve.

The exhaust turbine power generator 50 is connected to a portion of the exhaust pipe 30 and generates electric power by using exhaust gas from the internal combustion engine 10. More specifically, the exhaust turbine power generator 50 includes a turbine 51 and a generator 52 that is connected to an output shaft of the turbine 51. A gas inlet and a gas outlet of the turbine 51 are a turbine inlet portion 51I and a turbine outlet portion 51E, respectively. Exhaust gas from the internal combustion engine 10 is supplied to the turbine 51 through the turbine inlet portion 51I and the turbine 51 is rotated by the supplied exhaust gas. As the turbine 51 rotates, the generator 52 is driven and generates electric power. As described above, the exhaust turbine power generator 50 converts exhaust energy from the internal combustion engine 10 to electric energy.

The turbine outlet portion 51E of the turbine 51 is connected to a turbine downstream side exhaust pipe 60. Exhaust gas passing through the turbine 51 flows into the turbine downstream side exhaust pipe 60 from the turbine outlet portion 51E. A catalyst 80 for controlling exhaust gas is disposed in the middle of the turbine downstream side exhaust pipe 60.

The electric device 70 uses electric power generated by the exhaust turbine power generator 50. More specifically, the electric device 70 includes an inverter 71, a switch 72, a battery 73, and an electrical load 74. Electric power generated by the exhaust turbine power generator 50 is supplied to the battery 73 or the electrical load 74 after being converted by the inverter 71. Switching between supply of the electric power to the battery 73 and supply of the electric power to the electrical load 74 can be performed by using the switch 72. It is also possible to supply electrical power discharged from the battery 73 to the electrical load 74 by switching the switch 72. For example, in the case of a hybrid vehicle, the electrical load 74 includes a vehicle driving motor.

The control device 100 controls the operation of the internal combustion engine 10 and the electric device 70. Typically, the control device 100 is a microcomputer provided with a processor, a storage device, and an input and output interface. The control device 100 is also called electronic control unit (ECU). The control device 100 controls the operation of the internal combustion engine 10 by controlling the opening degree of the throttle valve 25, the timing of opening and closing of the intake valve and the exhaust valve, fuel injection, or the like. The control device 100 controls charging and discharging of the battery 73 and supply of electric power to the electrical load 74 by controlling the inverter 71 and the switch 72.

1-2. Two-System Exhaust Path

In the first embodiment, an exhaust path is divided into two systems. More specifically, as illustrated in FIG. 1, the exhaust pipe 30 is divided into a first exhaust pipe 30A (main exhaust pipe) and a second exhaust pipe 30B (sub-exhaust pipe). The first exhaust pipe 30A is connected to the cylinder 11 via a first exhaust opening portion 31A. Meanwhile, the second exhaust pipe 30B is connected to the cylinder 11 via a second exhaust opening portion 31B. That is, the cylinder 11 includes the first exhaust opening portion 31A and the second exhaust opening portion 31B.

The first exhaust pipe 30A is used to guide exhaust gas to the turbine 51 of the exhaust turbine power generator 50. Therefore, the first exhaust pipe 30A is disposed such that the first exhaust opening portion 31A and the turbine inlet portion 51I are connected to each other.

Meanwhile, the second exhaust pipe 30B is used to discharge exhaust gas in such a manner that the exhaust gas is discharged without passing through the turbine 51. Therefore, the second exhaust pipe 30B is disposed such that the second exhaust opening portion 31B and the turbine downstream side exhaust pipe 60 are connected to each other not via the turbine 51. That is, the second exhaust pipe 30B constitutes a bypass exhaust path that does not pass through the turbine 51. As illustrated in FIG. 1, the second exhaust pipe 30B is connected to the turbine downstream side exhaust pipe 60 at a bypass connection point 61. The bypass connection point 61 is positioned downstream of the turbine 51 and is positioned upstream of the catalyst 80.

FIG. 2 is a graph illustrating valve control in the first embodiment. The horizontal axis represents the crank angle and the vertical axis represents the lift amount of each valve. For description, the exhaust valve provided in the first exhaust opening portion 31A will be referred to as a “first exhaust valve” and the exhaust valve provided in the second exhaust opening portion 31B will be referred to as a “second exhaust valve”.

The first exhaust valve is opened and closed at usual timing. That is, the first exhaust valve is opened near the exhaust bottom dead center and the first exhaust valve is closed near the exhaust top dead center. Before the first exhaust valve is opened, in a combustion and expansion stroke in the internal combustion engine 10, the temperature and the pressure in the cylinder 11 are increased. Therefore, a high-temperature and high-pressure exhaust gas is discharged at a high speed that is close to the speed of sound immediately after the first exhaust valve is opened. An exhaust stream that is discharged at an initial stage of an exhaust stroke as described above is called a “blowdown stream”. Since the high-temperature and high-pressure blowdown stream is guided to the turbine 51 through the first exhaust pipe 30A, the driving efficiency of the turbine 51 is further increased.

The timing of opening of the second exhaust valve and the timing of closing of the second exhaust valve are later than the timing of opening of the first exhaust valve and the timing of closing of the first exhaust valve, respectively. Specifically, the second exhaust valve is opened near a time at which the blowdown caused by the first exhaust valve being opened ends and is closed near the exhaust top dead center. The maximum lift amount of the second exhaust valve is smaller than the maximum lift amount of the first exhaust valve.

1-3. Improvement in Turbine Work

FIG. 3 is a graph for describing a general change in exhaust pressure. The horizontal axis represents the crank angle and the vertical axis represents the pressure or the lift amount of an exhaust valve. At a time immediately after the exhaust valve is lifted, the area of an opening through which gas flows out is small since the valve lift amount is small. The speed of a gas stream is limited to the speed of sound. Therefore, there is a limit to the amount of exhaust gas that flows into an exhaust pipe immediately after the exhaust valve is lifted. Thereafter, exhaust gas gradually flows out as the valve lift amount increases. Therefore, as illustrated in FIG. 3, at the initial stage of the exhaust stroke, the exhaust pressure increases slowly. The tendency that the exhaust pressure slowly increases becomes further evident as the volume of the exhaust pipe increases.

The same matter will be discussed with regard to the configuration in the first embodiment illustrated in FIG. 1. The lift amount of the exhaust valve illustrated in FIG. 3 corresponds to the lift amount (refer to FIG. 2) of the first exhaust valve on the first exhaust opening portion 31A side in the first embodiment. There is a limit to the amount of exhaust gas that flows into the first exhaust pipe 30A immediately after the first exhaust valve is lifted. In this case, when the volume of the first exhaust pipe 30A is large, the exhaust pressure in the first exhaust pipe 30A increases slowly. In this case, the pressure of gas at the turbine inlet portion 51I of the turbine 51 also increases slowly.

In order to further increase the turbine work in the exhaust turbine power generating system 1, it is needed to further increase the expansion ratio of the turbine 51. In order to further increase the expansion ratio of the turbine 51, it is needed to further increase the pressure of gas at the turbine inlet portion 51I of the turbine 51. However, in a case where the volume of the first exhaust pipe 30A is large as described above, the exhaust pressure is unlikely to increase at the initial stage of the exhaust stroke and the pressure of gas at the turbine inlet portion 51I is also unlikely to increase.

FIG. 4 is a graph illustrating the dependency of turbine input work on the exhaust volume. The horizontal axis represents the exhaust volume divided by the volume of one cylinder and the vertical axis represents the turbine input work. Here, the expression “exhaust volume” means the volume of the first exhaust pipe 30A and the volume of a portion of the first exhaust pipe 30A between the first exhaust opening portion 31A and the turbine inlet portion 51I. The expression “the volume of one cylinder” means the volume of one cylinder 11. It can be understood from FIG. 4 that the turbine input work decreases as the exhaust volume increases.

As described above, in order to effectively guide energy of exhaust gas to the turbine 51 and to further increase the turbine work, it is preferable to set the volume of the first exhaust pipe 30A to be as small as possible. The exhaust turbine power generating system 1 according to the first embodiment is designed based on the above-described viewpoint.

FIG. 5 is a schematic diagram illustrating the characteristics of the exhaust turbine power generating system 1 according to the first embodiment. In FIG. 5, the electric device 70 and the control device 100 are not shown. The volume VA of the first exhaust pipe 30A is the volume of a portion of the first exhaust pipe 30A between the first exhaust opening portion 31A and the turbine inlet portion 51I. The volume VB of the second exhaust pipe 30B is the volume of a portion of the second exhaust pipe 30B between the second exhaust opening portion 31B and the bypass connection point 61. According to the first embodiment, the volume VA of the first exhaust pipe 30A is smaller than the volume VB of the second exhaust pipe 30B. For example, as illustrated in FIG. 5, in the case of the first exhaust pipe 30A and the second exhaust pipe 30B connected to the same cylinder 11, the length of the first exhaust pipe 30A is smaller than the length of the second exhaust pipe 30B. Alternatively, the diameter (sectional area of flow path) of the first exhaust pipe 30A is smaller than the diameter of the second exhaust pipe 30B.

As described above, in the exhaust turbine power generating system 1 according to the first embodiment, the volume VA of the first exhaust pipe 30A for guiding exhaust gas to the turbine 51 is relatively small. Therefore, the pressure of gas at the turbine inlet portion 51I becomes likely to increase and an increase in pressure of gas becomes large. That is, it is possible to effectively guide energy of exhaust gas (particularly, blowdown stream at initial stage of exhaust stroke) to the turbine 51 and to further increase the turbine input work (refer to FIG. 4). As a result, the expansion ratio of the turbine 51 increases and the turbine work in the exhaust turbine power generating system 1 is improved.

In the exhaust turbine power generating system 1 according to the first embodiment, the volume VB of the second exhaust pipe 30B that does not pass through the turbine 51 is relatively large. As the second exhaust pipe 30B becomes thick, pipe pressure loss becomes small and a force needed to push out exhaust gas from the cylinder 11 becomes small. That is, according to the first embodiment, it is possible to further reduce pumping loss.

2. Second Embodiment

FIGS. 6 and 7 schematically illustrate an example of the configuration of the exhaust turbine power generating system 1 according to a second embodiment of the present disclosure. In FIGS. 6 and 7, the electric device 70 and the control device 100 are not shown. The same description as in the first embodiment will be appropriately omitted.

In FIGS. 6 and 7, a plurality of cylinders 11-i (i=1 to 4) is illustrated. First exhaust pipes 30A-i and second exhaust pipes 30B-i are respectively connected to the first exhaust opening portions 31A and the second exhaust opening portions 31B of the cylinders 11-i. The first exhaust pipes 30A-i that respectively extend from the cylinders 11-i (i=1 to 4) are connected to the turbine inlet portion 51I after joining each other at a junction 33A. The second exhaust pipes 30B-i that respectively extend from the cylinders 11-i (i=1 to 4) are connected to the bypass connection point 61 on the turbine downstream side exhaust pipe 60 after joining each other at a junction 33B.

According to the second embodiment, arrangement of the first exhaust opening portions 31A and the second exhaust opening portions 31B of the cylinders 11-i is determined in consideration of the relative distance between each of the first exhaust opening portions 31A and the second exhaust opening portions 31B and the turbine inlet portion 51I. More specifically, for each of the cylinders 11-i, the first exhaust opening portion 31A is disposed closer to the turbine inlet portion 51I than the second exhaust opening portion 31B. In other words, one of the first exhaust opening portion 31A and the second exhaust opening portion 31B that is closer to the turbine inlet portion 51I is used as the first exhaust opening portion 31A for guiding exhaust gas to the turbine 51. In FIGS. 6 and 7, the first exhaust opening portion 31A is hatched.

A cylinder 11-2 will be used as an example. In an arrangement example illustrated in FIG. 6, one of two exhaust opening portions 31 of the cylinder 11-2 that is on the left side is close to the turbine inlet portion 51I and the other one of the two exhaust opening portions 31 that is on the right side is far from the turbine inlet portion 51I. Therefore, the exhaust opening portion 31 on the left side is used as the first exhaust opening portion 31A and the exhaust opening portion 31 on the right side is used as the second exhaust opening portion 31B. Meanwhile, in an arrangement example illustrated in FIG. 7, one of two exhaust opening portions 31 of the cylinder 11-2 that is on the right side is close to the turbine inlet portion 51I and the other one of the two exhaust opening portions 31 that is on the left side is far from the turbine inlet portion 51I. Therefore, the exhaust opening portion 31 on the right side is used as the first exhaust opening portion 31A and the exhaust opening portion 31 on the left side is used as the second exhaust opening portion 31B.

When the exhaust opening portions 31 are arranged as described above, it is easy to set the length of the first exhaust pipe 30A to be smaller than the length of the second exhaust pipe 30B. That is, it is easy to set the volume VA of the first exhaust pipe 30A to be smaller than the volume VB of the second exhaust pipe 30B.

3. Third Embodiment

FIGS. 8 and 9 are a sectional view and a side view for describing the characteristics of the exhaust turbine power generating system 1 according to a third embodiment of the present disclosure, respectively. The same description as in the above embodiments will be appropriately omitted.

In FIGS. 8 and 9, a direction from the internal combustion engine 10 to the turbine 51 is an X direction. The first exhaust pipe 30A extends such that the first exhaust pipe 30A is connected to the turbine 51 within the shortest distance in the X direction. The first exhaust pipes 30A-i that respectively extend from the cylinders 11-i join each other at the junction 33A (refer to FIGS. 6 and 7). In order to avoid a structure related to the first exhaust pipe 30A as described above, the second exhaust pipe 30B bypasses the structure in a Z direction that intersects the X direction. That is, the second exhaust pipe 30B is disposed to be offset from the first exhaust pipe 30A while being closer to the Z direction side than the first exhaust pipe 30A.

In an example illustrated in FIGS. 8 and 9, the Z direction is an upward direction and the second exhaust pipe 30B is disposed to be offset from the first exhaust pipe 30A while being closer to the upper side than the first exhaust pipe 30A. That is, the first exhaust pipe 30A and the second exhaust pipe 30B are divided into two (upper and lower) stages. The first exhaust pipe 30A on the lower stage is connected to the turbine 51 within the shortest distance. Meanwhile, the second exhaust pipe 30B on the upper stage is connected to the turbine downstream side exhaust pipe 60 after extending in the Z direction to avoid the first exhaust pipe 30A.

Since the second exhaust pipe 30B bypasses the structure as described above, a space for the shortest route to the turbine 51 is secured. Since it is possible to dispose the first exhaust pipe 30A in the space, it is easy to set the length of the first exhaust pipe 30A to be smaller than the length of the second exhaust pipe 30B. That is, it is easy to set the volume VA of the first exhaust pipe 30A to be smaller than the volume VB of the second exhaust pipe 30B.

4. Fourth Embodiment

As described above, immediately after the first exhaust valve is lifted, the area of an opening through which gas flows out is small since the valve lift amount is small. The speed of a gas stream is limited to the speed of sound. Therefore, there is a limit to the amount of exhaust gas that flows into the first exhaust pipe 30A immediately after the first exhaust valve is lifted. In order to increase the amount of exhaust gas as much as possible, in a fourth embodiment of the present disclosure, the first exhaust opening portion 31A is formed such that the area of the first exhaust opening portion 31A becomes as large as possible.

FIG. 10 is a schematic diagram for describing the characteristics of the fourth embodiment. The same description as in the above embodiments will be appropriately omitted. According to the fourth embodiment, layout is performed such that the area of the first exhaust opening portion 31A becomes as large as possible. However, there is a limit to the layout. For example, the diameter of the cylinder 11 (cylinder bore) is determined by the amount of exhaust gas or the number of cylinders. Generally, it is needed to make the intake opening portions 21 larger than the exhaust opening portions 31. In the fourth embodiment, the area of the first exhaust opening portion 31A is increased with the area of the second exhaust opening portion 31B being decreased. That is, the area of the first exhaust opening portion 31A is larger than the area of the second exhaust opening portion 31B.

Since the area of the first exhaust opening portion 31A is increased, the area of a curtain area immediately after the first exhaust valve is lifted is increased. Accordingly, the amount of exhaust gas that flows out at the initial stage of the exhaust stroke is further increased and the pressure of gas in the first exhaust pipe 30A is further increased. That is, an increase in pressure of gas in the blowdown stream becomes large and the turbine work is further increased.

5. Fifth Embodiment

Any of the first to fourth embodiments can be combined with each other as long as there is no contradiction. For example, for each of the cylinders 11-i illustrated in FIGS. 6 and 7, the area of the first exhaust opening portion 31A may be larger than the area of the second exhaust opening portion 31B. In this case, multiple effects can be achieved. 

What is claimed is:
 1. An exhaust turbine power generating system comprising: an internal combustion engine including a first exhaust opening portion and a second exhaust opening portion for each of cylinders; an exhaust turbine power generator configured to generate electric power by rotating a turbine by using exhaust gas from the internal combustion engine; a first exhaust pipe configured to connect the first exhaust opening portion and an inlet portion of the turbine; and a second exhaust pipe configured to connect the second exhaust opening portion and a turbine downstream side exhaust pipe downstream of the turbine, not via the turbine, wherein a volume of the first exhaust pipe is smaller than a volume of the second exhaust pipe.
 2. The exhaust turbine power generating system according to claim 1, wherein, in a case of the first exhaust pipe and the second exhaust pipe connected to the same cylinder, a length of the first exhaust pipe is smaller than a length of the second exhaust pipe.
 3. The exhaust turbine power generating system according to claim 2, wherein, for each of the cylinders, the first exhaust opening portion is disposed closer to the inlet portion of the turbine than the second exhaust opening portion.
 4. The exhaust turbine power generating system according to claim 2, wherein, in a case where a direction from the internal combustion engine to the turbine is a first direction and a direction intersecting the first direction is a second direction, the second exhaust pipe is disposed to be offset from the first exhaust pipe while being closer to the second direction side than the first exhaust pipe.
 5. The exhaust turbine power generating system according to claim 1, wherein a diameter of the first exhaust pipe is smaller than a diameter of the second exhaust pipe.
 6. The exhaust turbine power generating system according to claim 1, wherein an area of the first exhaust opening portion is larger than an area of the second exhaust opening portion. 